Method and system for providing spectrum sensing capability in a shared network

ABSTRACT

A method and system is provided for enabling spectrum sensing capability in a network having at least one primary user and a plurality of secondary users configured to communicate using a shared spectrum. The methods and systems include receiving values from sensors corresponding to received signal strength from a primary user in one or more frequencies of the shared spectrum. The values are used to interpolate at least one additional value between the sensors. A detection threshold is determined for sensing a signal transmitted from the primary user based on an acceptable amount of interference. The primary user is then determined to be transmitting in the one or more frequencies of the shared spectrum if any of the values received from the plurality of sensors or the at least one additional value interpolated along the path exceeds the detection threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/041,466, filed Jul. 20, 2018, which is a continuation of U.S.application Ser. No. 15/596,764, entitled “Method and System forProviding Spectrum Sensing Capability in a Shared Network,” filed May16, 2017, which claims the benefit of Provisional Application No.62/337,323 filed May 16, 2016, each of which is hereby incorporated byreference in its entirety.

FIELD OF INVENTION

The present invention relates to techniques for shared spectrum accessin wireless networks and, more particularly, to methods, systems, andapparatuses for providing spectrum sensing capability in such networks.

BACKGROUND

Radio frequency (RF) spectrum is the foundation for many wirelesscommunications systems in use today, including radar and cellularcommunications systems. Specified frequency ranges in the RF spectrum,sometimes identified as bands or channels, may be allocated for use bydifferent entities, for different purposes, or in different geographiclocations. As used in this disclosure, “spectrum” refers to anyfrequencies, frequency bands, and frequency channels in the RF spectrumthat may be used or allocated for wireless communications.

Because the available RF spectrum is finite, frequency allocations inthe spectrum are highly valued and often highly regulated. In the UnitedStates, for example, the Federal Communications Commission (FCC) and theNational Telecommunication and Information Administration (NTIA)regulate and manage spectrum allocations, allotments, and assignments.Frequency allocation is the process by which the entire RF spectrum isdivided into frequency bands established for particular types ofservice. These frequency allocations are then further subdivided intochannels designated for a particular service or “allotment.” Assignmentrefers to the final subdivision of the spectrum in which a party getsone or more frequency assignments, in the form of a license, to operatea radio transmitter on specific frequencies within a particulargeographic location.

The system of spectrum allocation, allotment, and assignment is failingto keep pace with the increasing demand for spectrum. Therefore there isa need to improve how available spectrum can be efficiently allocated,allotted, and assigned in the face of growing demand. Unless otherwisenoted, “allocation” is used in the present disclosure to generally referto the process by which spectrum is allocated, allotted, and assigned tolicensed users.

In view of this increasing demand for spectrum, a dynamic spectrumaccess (DSA) system may be used to share available spectrum amongmultiple users. A DSA system, for example, may include a Spectrum AccessSystem (SAS) that manages access to a shared spectrum, such as the 3.5GHz Federal band recently made available for shared commercial use inthe United States. In another example, a DSA system may be used to shareaccess to unlicensed spectrum, such as TV Whitespace. Coordinating andmanaging multi-user access to a shared spectrum present challenges in aDSA system.

As demand for spectrum grows, shared spectrum usage is becoming morecommon. In these environments, an SAS may control spectrum access amongusers assigned to different priority levels (or “tiers”) of spectrumaccess privileges. The SAS may implement spectrum management policiesfor users in each tier. For example, the SAS may be configured toprotect spectrum usage by higher-priority users (e.g., “primary users”)in shared bands from interference that would result from communicationsby lower-priority users (e.g., “secondary users”). As used herein, a“user” may refer to user equipment (e.g., a mobile phone, etc.), or anentity or person using user equipment. In many cases where there arerelatively few primary users, spectrum usage by primary users may below. Therefore, secondary users may dominate overall usage in thespectrum. However, whether in regions with high or low primary userspectrum usage, an SAS ensures that any spectrum allocations tosecondary users does not create unacceptable levels of interference withthe primary users transmitting in the shared spectrum.

A key feature of many DSA systems is the ability to identify primaryusers so they can be protected from harmful interference from secondaryusers. In some circumstances, primary users remain at fixed locationsand can therefore be registered in a database accessed by the SAS. Inthese cases, the SAS can use information from the database associatedwith the primary user, including location, system parameters, receiversensitivity, filtering, antenna height, pattern, azimuth, and elevation,to ensure that any secondary user assignment does not cause harmfulinterference to the primary user.

In other circumstances, primary users may not be static and may bemobile. Further still, primary users may be unable to share theirlocation and/or system parameters with an SAS for security orconfidentiality reasons. An example of one such primary user of thistype includes primary users operating federal radar systems on sea-goingmilitary vessels (e.g., military ships and submarines). To protect theseprimary users from secondary user interference, an SAS requires aspectrum sensing capability, for example, using an Environmental SensingCapability (ESC) system, to determine when and where the primary user isoperating and, optionally, determine system parameters associated withthe primary user. The SAS would leverage ESC system reports to ensure anacceptable quality of service for primary users transmitting in theshared spectrum, while also maximizing throughput and capacity for thesecondary users using the same spectrum. Moreover, the ESC system mayprovide operational security (OPSEC) and communications security(COMSEC), for example, to avoid compromising the locations and/or systemparameters of the primary users while also protecting them fromsecondary-user interference in the shared spectrum.

SUMMARY

In one aspect, the present disclosure is directed to a method forproviding spectrum sensing capability in a network having at least oneprimary user and a plurality of secondary users configured tocommunicate using a shared spectrum. In accordance with the disclosedembodiments of the invention, the method may include receiving, from aplurality of sensors positioned at different locations in the network,values corresponding to received signal strength from the at least oneprimary user in one or more frequencies of the shared spectrum, thelocations of the plurality of sensors defining a path. The method mayfurther include using the values received from the plurality of sensorsto interpolate at least one additional value corresponding to a receivedsignal strength at a location between sensors along the path,determining a detection threshold for sensing a signal transmitted fromthe at least one primary user based on an acceptable amount ofinterference, and determining that the at least one primary user istransmitting in the one or more frequencies of the shared spectrum ifany of the values received from the plurality of sensors or the at leastone additional value interpolated along the path exceeds the detectionthreshold.

In another aspect, the present disclosure is directed to a systemconfigured to provide spectrum sensing capability in a network having atleast one primary user and a plurality of secondary users configured tocommunicate using a shared spectrum. In accordance with the disclosedembodiments of the invention, the system may include a memory storinginstructions for execution by a processor. The processor may beconfigured to execute the stored instructions to receive, from aplurality of sensors positioned at different locations in the network,values corresponding to received signal strength from the at least oneprimary user in one or more frequencies of the shared spectrum, thelocations of the plurality of sensors defining a path. The processor mayfurther be configured to execute the stored instructions to use thevalues received from the plurality of sensors to interpolate at leastone additional value corresponding to a received signal strength at alocation between sensors along the path, to determine a detectionthreshold for sensing a signal transmitted from the at least one primaryuser based on an acceptable amount of interference, and to determinethat the at least one primary user is transmitting in the one or morefrequencies of the shared spectrum if any of the values received fromthe plurality of sensors or the at least one additional valueinterpolated along the path exceeds the detection threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this disclosure, illustrate various disclosed embodiments. Inthe drawings:

FIG. 1 is a schematic block diagram of an exemplary spectrum sensingsystem in accordance with the disclosed embodiments;

FIG. 2 is a schematic block diagram of an exemplary sensor that may beused in the spectrum sensing system of FIG. 1;

FIG. 3 is an exemplary configuration of the system according to FIG. 1including a plurality of sensors deployed along a coastline inaccordance with certain disclosed embodiments;

FIG. 4 is a flow chart illustrating an exemplary method for providingspectrum sensing capability in a network having at least one primaryuser and a plurality of secondary users communicating in a sharedspectrum in accordance with the disclosed embodiments;

FIG. 5 is a flow chart illustrating an exemplary method of defining aprotection zone and coordinating with one or more SASs to limit,relocate, or terminate RF transmissions of one or more secondary usersin a shared spectrum in accordance with the disclosed embodiments;

FIG. 6 is an exemplary configuration of the system according to FIG. 1including a protection zone that has been determined based on a primaryuser transmitting in one or more frequencies of a shared spectrum inaccordance with certain disclosed embodiments;

FIG. 7 is an exemplary configuration of the system according to FIG. 1which may be configured to estimate interference with one or moreprimary users transmitting in the shared spectrum in accordance withcertain disclosed embodiments;

FIG. 8 is an exemplary configuration of the system according to FIG. 1which may be configured to determine the protection zone based onestimated interference with the one or more primary users transmittingin the shared spectrum in accordance with certain disclosed embodiments;

FIG. 9 is a schematic block diagram illustrating exemplary inputs thatmay be used to determine the detection threshold in accordance with thedisclosed embodiments; and

FIG. 10 is a schematic block diagram illustrating exemplary inputs thatmay be used to determine a protection zone in accordance with thedisclosed embodiments.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

The following detailed description refers to the accompanying drawings.Wherever possible, the same reference numbers are used in the drawingsand the following description to refer to the same or similar parts.While several illustrative embodiments are described herein,modifications, adaptations and other implementations are possible. Forexample, substitutions, additions, or modifications may be made to thecomponents and steps illustrated in the drawings, and the illustrativemethods described herein may be modified by substituting, reordering,removing, or adding steps to the disclosed methods. Accordingly, thefollowing detailed description is not limited to the disclosedembodiments and examples. Instead, the proper scope of the invention isdefined by the appended claims.

FIG. 1 illustrates a schematic block diagram of an exemplary ESC system100 and may include, among other things, an ESC decision module 105 anda plurality of sensors 200. The sensors 200 receive RF signalstransmitted by at least one primary user in a shared spectrum and areconfigured to communicate with the ESC decision module 105 over a securedata link 115. The ESC decision module 105 may be configured to detectwhen the at least one primary user is transmitting over a singlefrequency and/or within a predetermined frequency channels (i.e., havingdefined frequency bandwidths) in the shared spectrum.

The ESC system 100 communicates with one or more SASs 120 at least whena primary user is detected transmitting within the shared spectrum. Forexample, the ESC decision module 105 may generate an indication that ithas detected a primary user using the shared spectrum and send theindication to the one or more SASs over a secure data link 125. The oneor more SASs may be configured to monitor the activity (e.g., RFtransmissions) of a plurality of secondary users in the shared spectrum,and may be further configured to relocate, suspend, and/or limit RFspectrum usage by the secondary users when the ESC system 100 indicatesthat it has detected a primary user transmitting in the shared spectrum.In one embodiment, the secondary users may include Citizens BroadbandService Devices (CBSDs), the primary users may include Federal IncumbentUsers (e.g., government or military users), and the shared spectrum mayinclude the 3.5 GHz Federal band. However, one skilled in the art wouldrecognize that in other embodiments the ESC system 100 may operate indifferent frequency bands and with different primary and secondaryusers.

In a preferred embodiment, the plurality of sensors 200 are distributedover a wide area and each communicates with the ESC decision module 105using a respective secure data link 115. Alternatively, the sensors 200may be configured to communicate with the ESC decision module 105through a common gateway, for example, directing all communications to asingle sensor 200 in communication with the ESC decision module. Thesecure data link 115 preferably includes a low-latency wireless or wiredinterface. In some embodiments, each of the sensors 200 may receive andprocess RF signals from at least one primary user, and may transmit tothe ESC decision module 105 values indicative of received signalstrengths that the sensor 200 determined in one or more frequenciesand/or frequency channels. The processing of RF signals received at eachsensor 200 for the purpose of determining values indicative of receivedsignal strengths may be performed within the sensor or at a locationremote from each sensor, or using a combination of local and remote dataprocessing.

Referring to FIG. 2, each sensor 200 may comprise hardware for receivingand processing RF signals, including for example an antenna 205, an RFlimiter 210, a filter 215, an amplifier 220, a transceiver 225, and acontroller 230. In the exemplary embodiments, the antenna 205 comprisesa 180-degree horizontal beamwidth and a 6 dBi gain. In some embodiments,the antennas 205 of a plurality of sensors 200 may monitor RF signalstransmitted within a wide geographic area and may include overlappingcoverage areas. In certain disclosed embodiments, each antenna 205 maybe generally directed perpendicularly with respect to an area in whichprimary users are expected to be transmitting and away from an area inwhich secondary users may be transmitting. For example, if the primaryusers are military ships at sea, the sensor antenna 205 may be locatedclose to a coastline and directed out to sea, whereas the secondaryusers would be positioned inland behind the antenna. In such anexemplary arrangement, a 180-degree antenna beamwidth may provide asuitable compromise between detecting at least one primary user's RFsignals while avoiding secondary-user interference from signalstransmitted in an area behind the antenna. Moreover, using a 180-degreebeamwidth antenna may prevent use of precision angle of arrival (AoA)estimates, thereby maintaining operational security (OPSEC) for theprimary users whose locations must remain uncertain.

The RF limiter 210 may be coupled to the antenna 205 to attenuate thereceived RF signal power and prevent potentially overloading thesensor's circuitry. The filter 215 may provide a bandpass filter thatonly allows received RF signals in a desired frequency band to pass. Inone disclosed embodiment, the passband of the filter 215 may be adaptedto pass signals between 3550-3650 MHz so that signals in the 3.5 GHzFederal band may be processed. The attenuated and filtered signals nextmay be processed by the amplifier 220, which may comprise a low noiseamplifier (LNA) configured to amplify the signal power prior to furtherprocessing by the transceiver 225. In one embodiment, thesignal-to-noise ratio provided by the LNA 220 is 5.5 dB and thetransceiver's digital bandwidth is 49 MHz. In this disclosed embodiment,the sensor 200 monitors frequencies in the 3.5 GHz band (e.g., 3550-3650MHz) and may switch between 3550-3600 MHz and 3600-3650 MHz sub-bands orbetween other sub-bands as appropriate for the implementation. Thesensor 200 may dwell for a period of time on each sub-band beforeswitching. In one exemplary embodiment, the sensor 200 may dwell on eachsub-band for thirty seconds before switching. This allows anynewly-transmitted signal in the 3550-3650 MHz band to be detected by thesensor 200 within sixty seconds.

The transceiver 225 may downconvert and sample the signal it receivesfrom amplifier 220 to create a digital baseband signal. The transceivermay send the digitized baseband signal samples to the controller 230 forfurther processing. Further to this disclosed embodiment, the controller230 may be configured to analyze the signals it receives fromtransceiver 225, determine one or more values indicative of receivedsignal strength corresponding to the signal, and communicate the valuesto the ESC decision module 105 over the secure data link 115. Thecontroller 230 may be implemented in various ways, for example, usingone or more field programmable gate arrays (FPGA), processors,application specific integrated circuits (ASICs), digital signalprocessors (DSPs), graphics processing units (GPUs), and/or centralprocessing units (CPUs). One skilled in the art would also appreciatethat the controller 230 may also include additional hardware andsoftware components, including for example a transmitter, one or moreprocessors, and a memory, which are not shown in FIG. 2.

The controller 230 preferably includes software and/or logic forprocessing the received signals and determining the values indicative ofsignal strength of the received RF signals. In some embodiments, eachsensor 200 preferably processes its own received signals using arespective controller 230. Alternatively, the sensor may employ acontroller 230 located remotely, for example, at another sensor, SAS, orother computer in the network. In some embodiments, the controller 230may comprise a channelizer for digitally channelizing the receivedbaseband signal into one or more frequency channels. For example, in apreferred embodiment, the channelizer may discretize the baseband signalinto individual, 10 MHz channels. The controller may further performcyclostationary processing of each channel, leveraging known propertiesof a primary user waveform to determine if signals from the primary userare present in the received signal. If the primary user is detected inthe received signal, based on the primary user's known signalproperties, the controller 230 may calculate a coarse estimate of asignal strength of the baseband signal. The coarse estimate of signalstrength may include values indicative of signal strength in one or morefrequencies and/or frequency channels, and the values may be representedas received signal strength indicator (RSSI) values. In this context, a“coarse” estimate does not place specific precision requirements on thedetermined RSSI values, although the disclosed embodiments may adjustthe precision of the RSSI values as desired for a given implementation.

The ESC decision module 105 receives the values indicative of signalstrength from the plurality sensors 200 and further processes thesereceived values to determine if a protection zone should be establishedto relocate, terminate, or limit secondary-user transmissions in a givenarea. A protection zone is implemented to reduce or eliminate potentialinterference with the RF signals of the primary user after the primaryuser has been detected by the ESC decision module. The ESC decisionmodule 105 may be implemented on one or more of the sensors 200, orpreferably the ESC decision module 105 may be implemented at a remotelocation relative to the sensors 200. Like the controller 230, the ESCdecision module 105 may be implemented using one or more processors,FPGAs, ASICs, DSPs, GPUs, and/or CPUs.

The ESC decision module 105 communicates with one or SASs 120 in orderto implement a protection zone. As described further below, each SAS hasthe ability to relocate secondary users to different frequencies orfrequency channels, terminate their transmissions on one or morefrequencies or frequency channels, and/or limit (e.g., restrict) thepermissible transmission power of certain secondary users. Each SAS 120may be configured to monitor secondary-user transmissions within acoverage area or for a number of secondary users. For example,information pertaining to secondary users may be maintained within anSAS database, which may include each registered secondary user within ageographic area or each registered secondary user within the control ofthe given SAS 120. In some embodiments, data related to the RF signalproperties and/or hardware of the primary users also may be available tothe ESC system 100 and may be used to determine a detection thresholdfor determining when a primary user is transmitting in a sharedspectrum.

Further to the disclosed embodiments, information pertaining tosecondary and/or primary users also may be obtained from third-partysystems, such as an FCC and/or Department of Defense (DOD) database 135.Alternatively, the ESC system 100 and/or the SASs 120 may storesecondary and/or primary user information in one or more databasesaccessible at the ESC system or SAS. In some embodiments, the ESC system100 may be programmed to recognize certain primary users without storingtheir related RF signal properties and/or hardware details.

In one exemplary embodiment, the ESC decision module 105 and each SAS120 may be implemented as software modules hosted on one or more cloudplatforms. A cloud platform may comprise any distributed system havingone or more software processes executed over a local or distributednetwork using at least one computer server or other computer hardware.The hardware may include computing devices (e.g., desktops,workstations, etc.), handheld computing devices, memory devices, networkcomponents, and/or interface components, which allow for network-basedcomputing and shared resources over a distributed network. Cloudservices are trusted by many of the largest federal and commercialenterprises in part because of the robust controls available to maintainsecurity and data protection on the cloud platform. A cloud platformalso provides flexibility with respect to resource allocation and remoteaccess. The ESC decision module 105 and SAS 120 may be implemented onthe same cloud platform or different cloud platforms that may beconfigured to communicate with one another.

Whether deployed on a shared cloud platform or on separate systems, theESC system 100 communicates with the one or more SASs 120 at least forthe purposes of communicating an indication that it has detected thepresence of a RF signal from a primary user in the shared spectrum, andfor obtaining information associated with secondary users within thecontrol of each SAS 120. Each SAS 120 preferably includes at leastlocation information and configuration data for each secondary userwithin its control. This information either may be stored in a databasemaintained by the SASs 120, or retrieved from one or more FCC/DODdatabases 135.

Each SAS 120 may communicate with other SASs 120 in order to share dataand communicate data to the ESC system 100. By sharing secondary-userinformation with the ESC system 100, the SAS 120 can provide informationto the ESC system 100 that enables the ESC decision module 105 todetermine a detection threshold for detecting a primary user. Thedetection threshold, discussed in more detail below, may be based on anacceptable level of interference from secondary users. SAS 120 mayprovide data pertaining to secondary users preferably to set a detectionthreshold that is the least intrusive to secondary users, whileminimizing interference with primary users in the shared spectrum. Afterthe ESC system 100 has detected a primary user using the sharedspectrum, the ESC system 100 can determine a protection zone (e.g.,corresponding to secondary users in a certain geographic area) anddirect one or more SASs 120 to terminate, relocate, and/or limittransmissions (e.g., constrain the transmit power and/or bandwidth) fromsecondary users within the protection zone. This allows the ESC system100 to determine and limit interference with primary users while primaryusers transmit in a spectrum shared with secondary users.

The information exchanged between SAS 120 and ESC system 100 may occurover a secure data link 125 using a wireless or wired interface and mayemploy a secure message protocol to maintain a desired level ofcommunications security (COMSEC). Likewise, the sensors 200 of the ESCsystem 100 may be connected to the ESC decision module 105 via a securedata link 115, including low-latency wireless or wired interfaces. Insome disclosed embodiments, the sensors 200 preferably send the ESCdecision module 105 one or more coarsely time-stamped RSSI valuescorresponding to RF signals the sensor received in one or morefrequencies or frequency channels. The ESC decision module 105 may usethe coarsely time-stamped RSSI values to detect RF transmissions by atleast one primary user in the one or more frequencies or frequencychannels of the shared spectrum. In an exemplary embodiment, the totaltime for a primary user detection event, including processing by thesensor 200, time for data transmission, processing by the ESC decisionmodule 105, and communication to one or more SASs 120, may take lessthan sixty seconds.

FIG. 3 shows an exemplary embodiment of the ESC system 100 in accordancewith an illustrative embodiment. A plurality of sensors 200 are deployedalong a coastline 310 separating land 300 from sea 305, wherein theantenna of each sensor 200 may be directed out to sea 305 to detectprimary users 10 transmitting in a shared spectrum. The sensors 200 maybe distributed over a wide area and communicate over secure data link115 to the ESC decision module 105. The ESC decision module 105communicates over secure data link 125 to one or more SASs 120 in orderto transmit detection events to the SASs 120 when a primary user 10 isdetected transmitting in the shared spectrum. In other words, when theESC decision module detects transmissions from at least one primaryuser, the ESC decision module may send an indication of such a detectionevent to the SASs 120, for example, alone or in combination with otherinformation provided to the SASs.

Each of the sensors 200 receives RF signals and processes the signalsbefore communicating values indicative of signal strength to the ESCdecision module 200. These values are based on the signal strength ofthe RF signal at each sensor location. In order to calculate valuesindicative of signal strength between the sensors 200, a path 315 isdefined between the sensors 200. The path 315 preferably includes one ormore linear segments from one sensor to another, each linear segmentcorresponding to a distance between different sensors. For example, thepath 315 may comprise a sequence of linear segments along the perimeterof a geographic area, such as along a coastline. The ESC decision module105 may use the path 315, together with the received signal strengthvalues, to calculate signal strength values between sensor locations. Inparticular, the ESC decision module 105 may interpolate signal strengthvalues along the path 315, including between adjacent sensors 200, ineach frequency and/or frequency channel being monitored, based on thesignal strength values that the ESC decision module received from thesensors 200 and the distances between sensors along the path 315. Thisprovides the ESC decision module 105 with calculated signal strengthvalues along a continuous path 315, where received and calculated signalstrength values can be compared to a detection threshold at eachlocation along the path 315, or at selected locations on the path.

FIGS. 4 and 5 provide flow diagrams outlining exemplary methods employedby the ESC decision module 105 in order to determine a detectionthreshold and then determine, from the detection threshold and receivedsignal strength values, whether a primary user is transmitting in theshared spectrum. In one exemplary embodiment, the ESC decision module105 may receive from the plurality of sensors 200 values indicative ofreceived signal strengths from RF transmissions of at least one primaryuser 10 transmitting in one or more frequencies or frequency channels ofthe shared spectrum (Step 405). The ESC decision module may determine apath 315 between the sensors 200 to interpolate at least one additionalvalue corresponding to a received signal strength between the sensors200 at a location along the path 315 (Step 410). The values may bequantized RSSI values processed by the sensors 200, where the RSSIvalues are provided for each frequency channel in a given frequencyrange. Moreover, the RSSI values may be coarsely time-stamped in orderto prevent back-calculation of the primary user's geographic location.Because they are coarsely time-stamped, the RSSI values may includetimestamps that are not sufficiently precise to be useful in trackinglocation (e.g., providing timestamps with a precision on the order ofhours or other relatively large blocks of time for each timestamp,rather than more precise timestamps with accuracies on the order ofseconds or less).

As values indicative of signal strength are received by the ESC decisionmodule 105, the values in each channel of the frequency range may becompared at each location along the path 315 to a detection threshold todetermine if a primary user 10 transmitted a signal in the sharedspectrum (Step 415). The detection threshold is a value calculated basedon an acceptable amount of interference with the primary user, which insome embodiments may be dependent on the amount of secondary useractivity and the primary user's signal characteristics and location. Ifthe detection threshold is exceeded (Step 420), the ESC decision modulewill determine a primary user is transmitting in the shared spectrum(Step 505), determine a protection zone, and communicate the protectionzone to the one or more SASs 120. The SASs implement the protection zoneto control secondary-user transmissions so as to reduce interferencewith the detected primary user.

To maximize secondary user capacity and performance while ensuringprimary user protection, ESC decision module 105 may set the detectionthreshold based on the amount of secondary user activity in an areaaround each sensor 200 or around each SAS 120. In determining thedetection threshold, a lower threshold may be overly-limiting onsecondary users operating in the area, while a higher threshold may notbe sufficient to prevent interference with primary-user signals in theshared spectrum. When an SAS registers high secondary user activity in agiven area (e.g., many secondary users transmitting in the sharedspectrum), or when primary users are expected to transmit from fartherdistances from the sensors 200, the ESC decision module 105 may set alower detection threshold. This will ensure primary users are detectedand their transmissions in the shared spectrum are not significantlyinterfered with by the high volume of secondary users in the area orwhen the primary users are located at greater distances from the sensors200 (e.g., when primary user signals may be attenuated based on pathloss between the primary user and an antenna in the sensor 200). Incontrast, a higher threshold may be used when secondary-user activity islow or when primary users are expected to be transmitting at closerdistances to the sensor 200. In one embodiment, the detection thresholdcan be set regardless of secondary user activity, for example, such thatthe ESC decision module 105 may set a “worst-case” scenario of secondaryuser activity. This may result in a lower detection threshold andgreater intrusion on secondary users operating in the area, but willensure primary users are protected from secondary user interference.

In a preferred embodiment, the detection threshold is determined in Step505 based on secondary user activity using actual secondary userlocation data as determined by each SAS 120. Secondary users mustregister with an SAS 120 in order to operate in a given area, and theSAS 120 can grant, deny, and/or limit requests to transmit in that area.Secondary-user location data and transmission characteristics are madeavailable to the SAS at least upon registration of the secondary userswith the SAS, and therefore can be used to determine actual secondaryuser activity in an area (e.g., as opposed to estimating or assuming“worst-case” secondary user activity). Alternatively, secondary useractivity may include estimating activity based on a deployment densityof secondary users and typical representations of secondary userparameters, including transmit power, antenna beamwidth and gain, andheight. Rather than using actual activity, an estimation may thereforebe used based on population or other data correlated with expectedsecondary user deployment. In either illustrative approach, the ESCdecision module 105 may have access to a secondary user database fromeach SAS 120, allowing the ESC system 100 to dynamically determinedetection thresholds at each location along the path 315 between sensorsand in each channel of a given frequency range.

Referring to FIG. 5, an exemplary method of defining a protection zoneis provided in accordance with the disclosed embodiments. Afterdetermining that one or more values indicative of signal strength exceedthe detection threshold, the ESC decision module 105 determines that aprimary user is transmitting in a shared spectrum (Step 505). In thissituation, a protection zone is determined, for example, by the ESCdecision module 105 (Step 510). The protection zone is an area whereSASs 120 are instructed to relocate, terminate, or limit secondary-usertransmissions to reduce or eliminate interference with the detectedprimary user's transmissions in the shared spectrum. After theprotection zone is determined in Step 510, at least one secondary usercan be identified (Step 515) in the protection zone. The SAS 120 canthen limit, relocated, or terminate transmissions from the at least oneidentified secondary user.

Referring to the exemplary embodiment in FIG. 6 and the methods of FIGS.4 and 5, the ESC system 100 may detect transmissions from primary users10 originating from an area monitored by the ESC sensors 200 (e.g.,transmissions from military ships at sea 305). Values indicative ofsignal strength (e.g., RSSI values) for the signals received at sensors200 are communicated to the ESC decision module 105. The ESC decisionmodule 105 may identify (or “activate”) a protection zone 600, which maybe defined as a subset of an industry- or government-defined exclusionzone 601, if the signal strength values exceed the detection threshold.Examples of industry-defined exclusions zones 601 include zones definedby the Wireless Innovation Forum (WINNF) or similar industry alliances.Examples of government-defined exclusions zones 601 include zonesdefined by the National Telecommunications and InformationAdministration (NTIA).

Aggregate interference to primary users 10 is limited to an acceptableamount of interference by SAS instructions to secondary users within theprotection zone 600. The instructions may direct certain secondary usersto move from a channel or frequency range that would cause unacceptableinterference with primary users transmitting in a given channel orfrequency range. The SAS 120 instructs secondary users to relocate todifferent channels or frequency ranges, to cease transmissions, or tolimit transmission power within the protection zone 600. Instructionsare sent using an SAS-to-secondary-user protocol that may be defined by,for example, WINNF. Following detection of a primary user, the SAS may,in some embodiments, confirm suspension, relocation, or limitation ofthe secondary user transmissions to the ESC system 100. In someembodiments, confirmation may occur as soon as 300 seconds after the ESCsystem 100 communicates the detection event to the SAS 120.

FIGS. 7 through 10 show exemplary systems and methods that may be usedto determine a detection threshold and an acceptable level ofinterference for primary users in accordance with certain disclosedembodiments. Sensors 200 of the ESC system 100 receive RF signals fromone or more primary users 10 and process the signals into valuesindicative of signal strength (e.g., RSSI values). The RSSI values arecommunicated to the ESC decision module 105, which interpolates the RSSIvalues reported by each sensor to calculate an RSSI estimate along apath 315 between the sensors 200. The interpolation results in anestimated RSSI value for each channel in the frequency range as afunction of a distance along the path 315 and at each location L (e.g.,RSSI(L)). The ESC decision module 105 then determines the detectionthreshold for each location along the path 315 based on SAS-reportedsecondary user activity. The determined detection threshold is functionof each sensor location, as well the quantity, location, andconfiguration of active secondary users. This ensures the detectionthreshold accounts for the aggregate interference created by secondaryuser activity. The interpolated RSSI(L) may then be compared to thedetection threshold at each location (L) in order to determine whether aprimary user is transmitting over a given frequency and/or frequencychannel (range of frequencies) in the shared spectrum, and whether aprotection zone should be determined to eliminate or minimizeinterference with the primary user. The following describes exemplarymethods for determining the detection threshold and acceptableinterference with a primary user's signal.

First, an acceptable interference with a known primary user signal isdetermined. In one example, an acceptable interference may calculatedfor an SPN-43 radar antenna of a primary user. Known characteristics ofthis radar antenna are utilized in the calculation, including a noisefigure (N/F) and an interference to noise ratio (I/N). In the case ofthe SPN-43 radar antenna, the ESC decision module 105 will use knownvariables of 3 dB for a noise figure and an interference to noise ratioof −6 dB at the radar receiver. Together with the Boltzmann constant(kTB), an acceptable interference level at the SPN-43 radar receiver maybe determined as shown in Equation (1); plugging in exemplary valuesresults in Equation (2):I _(A) =kTB+NF+I/N  (1)I _(A)=−114+3−6=−117 dBm/MHz  (2)

Using this value, a detection threshold may be determined to ensure thatthe aggregate interference due to secondary users at locations along thepath 315 between sensors 200 and received at the SPN-43 radar antenna isless than or equal to the acceptable interference.

For each location along the path 315, the ESC decision module calculatesthe aggregate interference based on the secondary users deployed withina specified distance 55 from the location along the path 315. Forexample, the distance 55 may be 150 kilometers from a location along thepath in this exemplary embodiment. The calculation of aggregateinterference may be calculated from actual secondary-user usage datafrom SASs, or may be performed assuming a worst-case number of secondaryusers transmitting within the specified distance 55. Such a worst-caseestimate may also assume the primary user is at a maximum usefuldistance 20 from the path 315 for its given hardware. In the case of theSPN-43 radar, it may be assumed for the worst-case scenario, that theradar is transmitting at a range of 65 nautical miles from the path 315.

To calculate aggregate interference in some embodiments, the ESCdecision module 105 may determine the number of secondary users within aradial 15 of the primary user signal, as shown in FIGS. 7 and 8. Theradial 15 is an area in which a signal from the primary user 10propagates. In particular, the ESC decision module 105 may firstdetermine RF transmission radials from a predetermined maximum usefuldistance 20 (e.g., 65 nautical miles) from the path 315 and passingthrough the path at a given set of locations. Characteristics of theprimary users' antennas are utilized, including the antenna's horizontalbeamwidth. In the case of the SPN-43 radar, the beamwidth 15 may be 1.75degrees. As shown in FIG. 7, the radials 15 from one or more primaryusers 10 may be calculated in this fashion. After determining the radial15 of the primary user or users 10, the ESC decision module 105 may usethe radials 15 to determine which secondary users 50 may potentiallycause interference to the primary users 10. Where several radials 15 arecalculated, a combined transmission area 30 may be determined based ontheir aggregate coverage areas as shown in FIG. 8. These secondary users50 located within this area 30 will be utilized in the determination ofaggregate interference.

Assuming there are N_(r) secondary users in the r^(th) radial, theeffective isotropic radiated power (EIRP) from each secondary user(CBSD_(n,r)) and in the direction of the primary user antenna is denotedEIRP_(CBSD) ^(SPN-43). As a worst-case estimate, the ESC decision modulecalculates the path loss between secondary user (CBSD_(n,r)) and alocation along the path, L, using free space path loss (“FSPL”). Theaggregate interference from L and from a particular radial, r, is thenestimated as Imax(L,r) below, where all quantities are expressed usinglinear scale.

$\begin{matrix}{{{Imax}\left( {L,r} \right)} = {\sum\limits_{n = 0}^{N_{r} - 1}\frac{{EIRP}_{{CBSD}_{n,r}}^{{SPN} - 43}}{{FSPL}\left( {CBSD}_{n,r}\rightarrow L \right)}}} & (3)\end{matrix}$

In this embodiment, the ESC decision module may then compute theaggregate interference Imax(L,r) across all radials 15 and at a locationalong the path 315 where the radials 15 intersect the path 315. Once theaggregate interference from secondary users is calculated, theprotection zone 600 can be determined. The interference due to aggregateinterference, Imax(L,r), by secondary users may then be calculated atthe primary user's location. Using the known characteristics of theprimary user and path loss (PL) from path 315 to the primary users,interference may be calculated as:I=Imax(L,r)−PL+Gradar−Lradar  (4)

Gradar is the gain of the primary user and Lradar is the radar receiverlosses of the primary user (e.g., due to cabling, etc.). For the SPN-43radar, Gradar is known as 32 dBi and Gradar is known as 2 dB. Therefore,I=Imax(L,r)−PL+32 dBi−2 dB=Imax(L,r)+30−PL. Setting interference (I)equal to the acceptable interference (I_(A)), the ESC decision modulecan calculate path loss (PL) for the SPN-43 radar. That is, the minimumPL for protecting the primary user radar receiver from aggregateinterference of secondary users (Imax(L,r)) based on a worst-casescenario can be obtained by solving for PL where I=I_(A).I=I _(A)kTB+NF+I/N=Imax(L,r)−PL+Gradar−Lradar−117 dBm/MHz=Imax(L,r)−PL+32 dBi−2 dBPL=147 dB+Imax(L,r) dBm/MHz  (5)

Therefore, path loss (PL) is a function of aggregate interference(Imax(L,r)) from secondary users at each location along the path betweensensors. In one example in which a single Category B rural CBSDsecondary user is located on the path, Imax(L,r)=37 dBm/MHz and, hence,PL=184 dBm/MHz.

A detection threshold may then computed for each location (L) along thepath and for each radial (r). The detection threshold DetThresh(L,r) ateast location and for each radial is calculated as a function ofeffective isotropic radiated power (EIRP) from the primary user lesspath loss (PL).DetThresh(L,r)=EIRPradar/MHz−PL  (6)

EIRP (i.e., effective isotropic radiated power) is a knowncharacteristic of a primary user and accessible or otherwise availableto the ESC decision module 105. For instance, the SPN-43 radar has aEIRP of 120 dBm/MHz. And using the example of one rural Category B CBSDwith Imax(L,r)=37 dBm/MHz, the detection threshold is calculated asfollows:DetThresh(L,r)=EIRPradar/MHz−PLDetThresh(L,r)=EIRPradar/MHz−(147 dB+Imax(L,r) dBm/MHz)DetThresh(L,r)=120 dBm/MHz−147 dB−Imax(L,r)DetThresh(L,r)=−27−Imax(L,r) dBm/MHzDetThresh(L,r)=−27−37 dBm/MHz=−64 dBm/MHz  (7)

Using this detection threshold (DetThresh(L,r)), a protection zone 600may then be determined by the intersection of the transmission area 30for which:RSSI(L)>DetThresh(L,r)  (8)

Therefore, where RSSI values exceed the detection threshold along thepath 315 defined between sensors 200, a protection zone 600 isdetermined as defined by the transmission area 30 extending over one ormore secondary users 50. The ESC system 100 may alert the SASs 120 inthe protection zone 30 of the detection event, and the SASs may thenrelocate, limit, or terminate transmissions from the secondary users 50in the protection zone 30.

FIGS. 9 and 10 show exemplary inputs for calculating the detectionthreshold 920 and the protection zone 600 in accordance with certaindisclosed embodiments. The detection threshold (DetThresh(L,r)) iscalculated for each location along the path 315 between sensors and foreach radial 15 of the primary user 10. Inputs for the detectionthreshold, as described above, include the acceptable interference (I)905 with the primary user, the effective isotropic radiated power (EIRP)910 of the primary user, and the aggregate interference (Imax(L,r)) 915from secondary users. After the detection threshold is calculated, adetection event can be triggered when the values indicative of signalstrength exceed the detection threshold at a given location along thepath 315 between sensors. If exceeded, the ESC decision module 105 mayuse inputs including secondary-user characteristics 1005 (e.g.,aggregate interference (Imax(L,r)), etc.) and primary usercharacteristics 1010 (e.g., horizontal beamwidth, etc.) to determine aprotection zone 600. One or more SAS can relocate, limit, or terminateone or more secondary users in the protection zone 600.

In order to maintain operational security of primary users, thedetection threshold and calculated interference with the primary userdoes not allow the exact position of the primary user to be determinedif the ESC system is compromised. More specifically, at no point duringa detection event does the ESC system 100 predict or estimate thepropagation loss from the primary user. This avoids creating an inputfor geolocation computation of the primary user. Moreover, at no pointis the location of a primary user accurately estimated or tracked. Inthis manner, the ESC system 100 does not compute or reveal anyinformation pertaining to the location or movement of any primary usertransmitting in a shared spectrum.

Therefore, the ESC system 100 is designed to operate without anyconnectivity to any sensitive database or system of a primary user(e.g., military or federal primary user). The ESC system 100 also doesnot store, retain, transmit, or disclose operational informationregarding the movement or position of any primary user or anyinformation that reveals other operational information that is notrequired to effectively determine a detection threshold, establish aprotection zone, and compare signal strength values to the detectionthreshold.

To maintain operational security, the ESC system 100 will only reportcoarsely timestamped, quantized signal strength measurements to the SAS120. These measurements will not be stored or retained by the ESCsensors 200 or the ESC decision module 105. Processing of signalstrength measurements will be limited to comparison of the measuredsignal strength values against the detection threshold. Furthermore, theESC system 100 will not store or transmit any time-series data fordetected primary users, store or transmit signal waveformcharacteristics from a primary user, time-stamp measurements withprecision sufficient to enable Time Difference of Arrival geolocationtechniques, or employ sensors with receivers or antennas capable ofprecise angle or arrival estimation.

Additionally, to prevent unintended disclosure of operationalinformation on the movement or position of any primary user, the ESCsystem 100 will maintain a position estimate uncertainty in the range of25-65 nautical miles. In order to accomplish this, the detectionthreshold calculation assumes a reciprocal path loss for RF signals froma primary user to an ESC sensor 200, and to a primary user from an ESCsensor 200. propagation. At no point during a detection event does theESC system 100 predict or estimate the primary user's propagation loss,which is a necessary input to a geolocation computation.

Reciprocal path loss relies on the observation that propagation lossfrom a distant primary user (e.g., from a radar) to a sensor locationwill be equal to or less than the propagation loss from the sensorlocation to the same primary user (e.g., to a radar receiver). Thereforethe path loss determined for signals transmitted from a primary user 10to a sensor 200 is assumed to equal the path loss for signalstransmitted in the opposite direction from the sensor 200 to the primaryuser 10. Therefore, the ESC decision module 105 need only establish anappropriate signal reception level (i.e., the detection threshold) fromthe primary-user transmission to determine if the aggregate signaltransmissions from secondary users to the primary user will exceed anacceptable limit. To establish the detection threshold, the ESC decisionmodule 105 models the propagation loss from the location of eachsecondary user to a location along the path 315 where the outgoingpropagation loss to the primary user can be applied. Using thisapproach, the only signal processing conducted by the ESC decisionmodule 105 and sensor 200 is interpolation of the signal strength valuesand comparison of the interpolated data against a determined detectionthreshold.

While ensuring end-to-end security, if an adversary were to obtain RSSImeasurements from multiple sensors 200 and the adversary had knowledgeof the location of the sensor 200, it could at most performtrilateration for coarse incumbent position estimation. Trilaterationrelies on distance estimates from three or more sensors. An adversarymay estimate distance from each sensor 200 to a primary user 10 usingthe RSSI values, sensor position, and a link budget analysis. Thefollowing variables would be used as inputs to the link budget analysiswould be Radar Transmit Power (P_(T)), Propagation Loss (P_(L)), andSensor Antenna Gain (G_(R)). Radar Transmit Power depends on conductedpower and radar antenna gain in direction of sensor. Propagation Lossdepends on clutter loss (e.g., reflection off structures near radar,sensor), sea state, atmospheric conditions (e.g., ducting), terrain,buildings, etc. And Sensor Antenna Gain depends on sensor antenna gainin direction of radar. The link budget analysis would be used toestimate the P_(L) providing the measured RSSI. From P_(L) and apropagation model providing the relationship between P_(L) and distance,distance could be estimated as follows:RSSI=P _(T) +P _(T) +G _(R)PL=RSSI−P _(T) −G _(R)  (9)

Propagation loss can then be used to estimate distance. However, thereare several uncertainties involved in the distance estimation andtrilateration process. These uncertainties derive from (1) estimationsused for radar conducted power and antenna gain, (2) estimates used forsensor antenna gain, (3) the propagation model employed (e.g., clutter,sea-state, atmospheric conditions), and (4) integration periodmisalignments with radar pulses in both time and space. Theseuncertainties will typically lead to an RSSI estimate that hasuncertainty characterized by a standard deviation of more than 5 dB.Subsequent use of these RSSI values to estimate distance therefore leadsto a large extrapolated distance uncertainty.

To illustrate how distance uncertainties may lead to trilaterationuncertainty, a Monte Carlo simulation using four sensors equally spacedby 50 kilometers along the coastline and a primary user 50 kilometersoffshore has been shown to result in position estimate with a standarddeviation around 25 km. The simulation assumptions included using a freespace path loss assumption and a measured RSSI value that is Gaussian,with a mean given by the exact RSSI and standard deviation of 2 dB. Inmost deployments, however, the RSSI standard deviation will be at least5 dB. In addition, one will not know the precise relationship betweendistance and path loss given the limited fidelity of existingpropagation models. As a result, the position estimate uncertainty ofthe ESC system 100 using a trilateration process to estimate thelocation of the primary user 10 will typically exceed 50 km.

In addition to operational security, the ESC system includes safeguardsto maintain communications security. In particular, the ESC system 100includes an architecture that ensures unauthorized parties cannot accessor alter the ESC components or software, access or alter individualsensors, or otherwise corrupt the operation of the ESC system. Threatsto the ESC include unauthorized access, alteration, or corruption of ESCsoftware functions, unauthorized use of the sensors, and intrusionand/or tampering with sensor hardware, software, or functions.Additional security threats include Internet-connected devices that mayprobe an SAS via spectrum access queries and, as a result, learninformation about primary users (e.g., location, movement, spectrum use,etc.) at a higher level of fidelity than can be discovered through otherpublicly available information sources (e.g., news reports about navalactivity).

The ESC system 100 deploys at least the following measures to ensurethat ESC decision module 105, sensor 200, and SAS 120 operations are notcompromised by attack, damage, or unauthorized access. Softwarefunctions for the ESC system (e.g., the ESC decision module) and the SASmay be hosted in a secure cloud environment. Moreover, to preventunauthorized use, each sensor 200 may employ a secure boot function toensure that the sensor 200 can only be operated when authenticated by,and communicating with, the ESC decision module. Each sensor 200 mayalso use an intrusion monitor to sense when the a physical portion ofthe sensor or system is opened by an unauthorized entity. The sensors200 may also contain a compass to determine the orientation of thesensor. When unauthorized intrusion or an unexpected orientation changeis sensed, an alert in the ESC system 100 can be triggered to takeappropriate measures (e.g., deactivate the compromised ESC sensor,trigger an alarm signal, etc.).

In addition, the communications between the ESC system 100 and SASs 120,and between SASs 120, are secure. A proprietary interface between theESC and the SAS may be used when signals are conveyed between the ESCdecision module 105 and the one or more SASs 120. Secure communicationsbetween the SAS 120 and ESC system 100 may include use ofindustry-recognized PM certificates, which include a hierarchical set ofroles, policies, and procedures needed to mutually authenticate, create,manage, distribute, use, store, and revoke digital certificates andmanage public-key encryption. The purpose of the PM structure is tofacilitate legitimate electronic communications between the SASs 120 andthe ESC system 100 in a secure manner. To protect the exchange ofinformation and communications between the SAS and ESC system, TLS—aprotocol created to provide authentication, confidentiality, and dataintegrity between two communicating applications—may also be used withthe PM structure.

In addition to communications and operational security, the deploymentof sensors 200 may be organized so as to maintain security and tomaximize coverage of a particular region where primary users areexpected to be transmitting. ESC system equipment may be installed oncommercially available communications towers, building rooftops, poles,or other structures that are sufficiently elevated with respect to localclutter, and where the sensor antennas may be provided an unobstructedline-of-sight to the horizon. Each sensor deployment location isselected to ensure it meets access and physical security requirementsnecessary to ensure the sensor is operated in a safe and secure manner,and that the general public and unauthorized persons cannot gain accessto the sensor. While exemplary examples of sensor deployment locationsprovided here include coastal areas, it is understood that sensors canbe installed in any region in which the detection of primary users isdesired (e.g., along inland location). Further, while the disclosedembodiments are described as including a plurality of sensors 200, thoseskilled in the art will appreciate that certain aspects disclosed hereinalso may be implemented with deployments having only a single ESC sensor200.

Each sensor may be handled and installed by professional installers. Theinstallation team preferably follows industry standard processes toensure that sensors are securely handled and installed on sites. Accessto site facilities may be limited to authorized personnel, contractorsor subcontractors, and persons authorized to access the site by thefacility owner or authorized manager. All sensor installationspreferably complies with government rules governing wireless facilitysiting.

The ESC sensors are ideally positioned at locations above averageterrain to allow for unobstructed views of a region to be monitored. Inexemplary deployments, ESC sensors 200 may be spaced on average thirtyto forty kilometers apart, and the precise sensor deployment locationswill be determined to ensure that at least three sensors are capable ofsensing each location in the region to be monitored 50 km from the pathdefined between the sensors. The use of multiple sensors results in aresilient, high-availability system and ensures that the ESC system canreliably detect primary user transmissions.

While illustrative embodiments have been described herein, the scope ofany and all embodiments having equivalent elements, modifications,omissions, combinations (e.g., of aspects across various embodiments),adaptations and/or alterations as would be appreciated by those skilledin the art based on the present disclosure. The limitations in theclaims are to be interpreted broadly based on the language employed inthe claims and not limited to examples described in the presentspecification or during the prosecution of the application. The examplesare to be construed as non-exclusive. Furthermore, the steps of thedisclosed routines may be modified in any manner, including byreordering steps and/or inserting or deleting steps. It is intended,therefore, that the specification and examples be considered asillustrative only, with a true scope and spirit being indicated by thefollowing claims and their full scope of equivalents.

What is claimed is:
 1. A method for providing spectrum sensingcapability in a region having at least one primary user and at least onesecondary user configured to communicate using a shared spectrum, themethod comprising: receiving signals from a plurality of sensorspositioned at different locations in the region; determining, based onthe received signals, values corresponding to received signal strengthfrom the at least one primary user in one or more frequencies of theshared spectrum, using the values determined based on the receivedsignals from the plurality of sensors to determine the area in which aprimary user is active; determining a threshold based on data associatedwith the at least one secondary user; determining that the at least oneprimary user is transmitting in the one or more frequencies of theshared spectrum upon any of the values determined based on the receivedsignals from the plurality of sensors exceeding the threshold; andidentifying a secondary user whose transmit power must be limited in theone or more frequencies based on the determination that the at least oneprimary user is transmitting in the one or more frequencies.
 2. Themethod of claim 1, wherein the one or more frequencies of the sharedspectrum correspond to one or more frequency channels, and the valuescorresponding to received signal strength are determined throughcyclostationary processing of each channel based on known properties ofa primary user waveform.
 3. The method of claim 1, wherein the valuescorresponding to received signal strength are determined usingcyclostationary processing based on known properties of a primary userwaveform.
 4. The method of claim 1, wherein the values corresponding toreceived signal strength comprise Received Signal Strength Indicator(RSSI) values.
 5. The method of claim 4, wherein the valuescorresponding to received signal strength further comprise time-stampedRSSI values.
 6. The method of claim 1, further comprising: determining aprotection zone in the region based on the determination that the atleast one primary user is transmitting in the one or more frequencies ofthe shared spectrum; and identifying a secondary user in the protectionzone whose transmit power must be limited in the one or morefrequencies.
 7. The method of claim 6, wherein the protection zone isfurther determined based on characteristics of a signal transmitted fromthe at least one primary user.
 8. The method of claim 7, wherein thesignal characteristics include a direction or a beam width.
 9. Themethod of claim 6, further comprising: receiving information regardingthe at least one secondary user in the region from a Spectrum AccessSystem (SAS); and identifying the secondary user in the protection zonewhose transmit power must be limited in the one or more frequenciesbased on the information received from the SAS.
 10. The method of claim1, further comprising: determining a path loss for signals transmittedfrom the at least one primary user to a sensor in the plurality ofsensors; and using the determined path loss to determine the threshold.11. The method of claim 10, wherein the path loss determined for signalstransmitted from the at least one primary user to the sensor in theplurality of sensors is assumed to equal the path loss for signalstransmitted in the opposite direction from the sensor to the at leastone primary user.
 12. The method of claim 1, wherein determining thatthe at least one primary user is transmitting in the one or morefrequencies of the shared spectrum is performed without compromising thelocation of the at least one primary user in the region.
 13. The methodof claim 1, further comprising instructing a Spectrum Access System(SAS) to limit, relocate, or terminate the at least one secondary userusing the one or more frequencies in the region if it is determined thatthe at least one primary user is transmitting over the one or morefrequencies.
 14. The method of claim 1, wherein the at least onesecondary user comprises a Citizens Broadband Service Device (CBSD). 15.The method of claim 1, wherein an acceptable amount of interference isdetermined based on a noise figure and an interference-to-noise ratiocorresponding to a signal transmitted from the at least one primaryuser.
 16. The method of claim 1, further comprising: determining anaggregate amount of interference based on data associated with aplurality of secondary users; and determining the threshold such thatthe aggregate amount of interference is less than or equal to anacceptable amount of interference.
 17. The method of claim 16, furthercomprising: calculating the aggregate amount of interference at a sensorin the plurality of sensors using a path loss of one or more secondaryusers located within an area, wherein the area is determined based oncharacteristics of a signal transmitted from the at least one primaryuser.
 18. A system configured to provide spectrum sensing capability ina region having at least one primary user and at least one secondaryuser configured to communicate using a shared spectrum, the systemcomprising: a memory storing instructions for execution by a processor;and a processor configured to execute the stored instructions to:receive signals from a plurality of sensors positioned at differentlocations in the region; determine, based on the received signals,values corresponding to received signal strength from the at least oneprimary user in one or more frequencies of the shared spectrum, use thevalues determined based on the received signals from the plurality ofsensors to determine the area in which a primary user is active;determine a threshold based on data associated with the at least onesecondary user; determine that the at least one primary user istransmitting in the one or more frequencies of the shared spectrum uponany of the values determined based on the received signals from theplurality of sensors exceeding the threshold; and identify a secondaryuser whose transmit power must be limited in the one or more frequenciesbased on the determination that the at least one primary user istransmitting in the one or more frequencies.
 19. The system of claim 18,wherein the one or more frequencies of the shared spectrum correspond toone or more frequency channels, and the values corresponding to receivedsignal strength are determined through cyclostationary processing ofeach channel based on known properties of a primary user waveform. 20.The method of claim 18, wherein the values corresponding to receivedsignal strength are determined using cyclostationary processing based onknown signal properties of a primary user waveform.
 21. The method ofclaim 18, wherein the values corresponding to received signal strengthcomprise Received Signal Strength Indicator (RSSI) values.
 22. Themethod of claim 21, wherein the values corresponding to received signalstrength further comprise time-stamped RSSI values.
 23. The system ofclaim 18, wherein the processor is further configured to: determine aprotection zone in the region based on the determination that the atleast one primary user is transmitting in the one or more frequencies ofthe shared spectrum; and identify a secondary user in the protectionzone whose transmit power must be limited in the one or morefrequencies.
 24. The system of claim 23, wherein the protection zone isfurther determined based on characteristics of a signal transmitted fromthe at least one primary user.
 25. The system of claim 24, wherein thesignal characteristics include a direction or a beam width.
 26. Thesystem of claim 23, wherein the processor is further configured to:receive information regarding the at least one secondary user in theregion from a Spectrum Access System (SAS); and identify the secondaryuser in the protection zone whose transmit power must be limited in theone or more frequencies based on the information received from the SAS.27. The system of claim 18, wherein the processor is further configuredto: determine a path loss for signals transmitted from the at least oneprimary user to a sensor in the plurality of sensors; and use thedetermined path loss to determine the threshold.
 28. The system of claim27, wherein the path loss determined for signals transmitted from the atleast one primary user to the sensor in the plurality of sensors isassumed to equal the path loss for signals transmitted in the oppositedirection from the sensor to the at least one primary user.
 29. Thesystem of claim 18, wherein determining that the at least one primaryuser is transmitting in the one or more frequencies of the sharedspectrum is performed without compromising the location of the at leastone primary user in the region.
 30. The system of claim 18, furthercomprising instructing a Spectrum Access System (SAS) to limit,relocate, or terminate the at least one secondary user using the one ormore frequencies in the region if it is determined that the at least oneprimary user is transmitting over the one or more frequencies.
 31. Thesystem of claim 18, wherein the at least one secondary user comprises aCitizens Broadband Service Device (CBSD).
 32. The system of claim 18,wherein the processor is further configured to determine an acceptableamount of interference based on a noise figure and aninterference-to-noise ratio corresponding to a signal transmitted fromthe at least one primary user.
 33. The system of claim 18, wherein theprocessor is further configured to: determine an aggregate amount ofinterference based on data associated with a plurality of secondaryusers; and determine the threshold such that the aggregate amount ofinterference is less than or equal to an acceptable amount ofinterference.
 34. The system of claim 33, wherein the processor isfurther configured to: calculate the aggregate amount of interference ata sensor in the plurality of sensors using a path loss of one or moresecondary users located within an area, wherein the area is determinedbased on characteristics of a signal transmitted from the at least oneprimary user.
 35. A non-transitory computer readable medium storinginstructions for execution by at least one processor, the instructionswhen executed being configured to cause the at least one processor toperform a method for providing spectrum sensing capability in a regionhaving at least one primary user and at least one secondary userconfigured to communicate using a shared spectrum, the methodcomprising: receiving signals from a plurality of sensors positioned atdifferent locations in the region; determining, based on the receivedsignals, values corresponding to received signal strength from the atleast one primary user in one or more frequencies of the sharedspectrum, using the values determined based on the received signals fromthe plurality of sensors to determine the area in which a primary useris active; determining a threshold based on data associated with the atleast one secondary user; determining that the at least one primary useris transmitting in the one or more frequencies of the shared spectrumupon any of the values determined based on the received signals from theplurality of sensors exceeding the threshold; and identifying asecondary user whose transmit power must be limited in the one or morefrequencies based on the determination that the at least one primaryuser is transmitting in the one or more frequencies.
 36. The method ofclaim 1, wherein the data associated with the at least one secondaryuser comprises signal strength.
 37. The system of claim 18, wherein thedata associated with the at least one secondary user comprises signalstrength.
 38. The non-transitory computer readable medium of claim 35,wherein the data associated with the at least one secondary usercomprises signal strength.
 39. The method of claim 10, wherein the pathloss is a function of aggregate interference from a plurality ofsecondary users.
 40. The system of claim 27, wherein the path loss is afunction of aggregate interference from a plurality of secondary users.